Still have picture from dealing with poor designs on my Fleetwood.
ANYTHING is better, than 2 staples holding a "toothpick" frame in corners.
What holds it is plywood glued to the frame, but with the age the glue softens, some water damage can enter and whole thing starts going apart.
What you see on the picture is my 2nd camper repair, when the sides start sagging too much.
At the bottom is the repair I did like 5 years earlier, when rotten 3/4 by 1.5 frame was replaced with 6" tall board and metal corners were added. That hold just fine after 5 years and on the 2nd repair I did not have to touch it.
Now going higher on the frame - you can see that whole front of the camper rest on two .75 x1.5 pieces of frame. That, combined with some water intrusion over the years made the sides sagging and eventually jacks start rattling on the mounts. Funny part, the camper is advertised as "aluminium frame", when you don't see any aluminium on this wall.
I replaced lower 1.5" tall piece with 4" piece cut to shape and added diagonal frame in upper corners.
That was done 3 years ago and I still use the camper.

Click For Full-Size Image.